Big-Block Cylinder Head Flow Testing

Cylinder head porting is often equated with time and expense, and we've all heard horror stories about porting through the casting and ruining the cylinder head. For these reasons, many enthusiasts are hesitant to port their own heads, due to a lack of experience, and reticent to have the engine builder or machine shop perform the work for fear of adding expense to the rebuild. But while extensive race-style porting jobs can take many hours of grinding, sanding, and testing to perform correctly, the fact is that most of the benefit of a port job can be seen in just a couple of hours per cylinder.

For most bracket, street, or dual purpose cars, spending a little time on the cylinder head ports can greatly improve flow, increasing the engine's power substantially without killing your budget. In our experience, most factory heads will gain a significant increase in flow simply by matching the ports to the intake and header, and cleaning up areas like where the pushrod “pinches” into the intake port and the bowl area under the valves. Performing a little port work is especially beneficial if your engine will be equipped with a high-flowing intake manifold and headers, since the ports (especially in factory heads) can become the most restrictive part of the engine.

To prove our theory, we decided to flow the intake and exhaust runners of several popular factory cylinder heads and then port an intake and exhaust runner to compare the difference. We'll be performing our testing on the Superflow flow bench at Auto Performance Engines, so the numbers you see are real-world flow numbers for popular Mopar big-block cylinder heads. For comparison, we'll also flow two popular aftermarket heads, the 440 Source Stealth and Edelbrock Performer RPM, then port the intake and exhaust runners of the Edelbrock head and measure the difference on the flow bench.

Remember that we're not out to gain every last cfm of airflow through these heads, we simply want to show what spending a little time on the ports will produce in terms of flow numbers. To keep our testing legitimate, we will only spend one hour porting and polishing each runner, which will only allow us to hit the above mentioned beneficial areas and clean up the casting flashing of the runners, bowls, and areas under the valve seat. We also stayed with the factory valve sizes for both the factory and aftermarket cylinder heads, as increasing valve size and performing trick, multi-angle valve jobs is a whole other area in terms of cylinder head work.

While it is tempting to get crazy with the grinder while porting heads, removing too much material from the ports not only risks damaging the heads, but significantly increases the volume of the runner which is not so good for low and mid-range torque. So rather than whittling away a considerable portion of the runners for maximum high-end flow, we're removing a reasonable amount of material and cleaning up key areas that should improve power throughout the normal rpm range of a street engine.

Follow along, and after showing you the flow numbers for three factory and two aftermarket cylinder heads, we'll show you why spending a little time porting key areas of your cylinder heads can really pay off.

Stock/Out of the Box Flow Numbers:

For our baseline numbers, and to let you know what a variety of stock and aftermarket heads flow in untouched form, we commandeered the flow bench at Auto Performance Engines. Remember that flow benches are like dynos and there are slight variances between machines and conditions. We're not trying to demonstrate how well or poorly certain cylinder heads flow, just provide a comparison between heads and show the benefits of a little port work.

The added benefit of porting

To demonstrate how spending just an hour per port can really help cylinder head flow, we began grinding and polishing the intake and exhaust port of our 452 casting factory head while Kevin at APE did the same with the Edelbrock Performer RPM. It was then back to the flow bench to see what affect our port work had on intake and exhaust flow.

11/12<STRONG>9</STRONG> The APE ported Edelbrock head showed improvement on the flow bench as well, with an impressive 305 cfm on the intake side at .700 lift. Exhaust flow improved from 232 cfm to 244 cfm, also at .700 lift. Average flow was up significantly as well, indicating that time porting cylinder heads is definitely time well spent.

Summation:

From our tests, it is pretty obvious that even the best un-ported factory big-block Chrysler cylinder heads leave a lot to be desired when compared to mildly ported versions or aftermarket heads. Also, while the percentage of flow gained by porting was greater on the factory head, the aftermarket heads start off a lot better, so it's more difficult and time consuming to make big gains. Any of the cylinder heads we tested could certainly be made to flow better, but we limited the time we spent on port work to more closely imitate what the majority of our readers would do, or could afford.

12/12<STRONG>10</STRONG> We wanted to show you a comparison shot of two intake ports as well. The port on the right was treated to a complete porting job, all the way down into the chamber. While not necessarily wanting to make the port larger, simply cleaning up the port will achieve gains in flow. The intake port on the left has received just a simple